CN114477920A

CN114477920A - Green environment-friendly light high-strength concrete

Info

Publication number: CN114477920A
Application number: CN202210252317.9A
Authority: CN
Inventors: 段平娥; 张召伟
Original assignee: Hunan Xianfeng Building Material Co ltd
Current assignee: Fujian Dingjie Concrete Products Co ltd
Priority date: 2022-03-15
Filing date: 2022-03-15
Publication date: 2022-05-13
Anticipated expiration: 2042-03-15
Also published as: CN114477920B

Abstract

The invention discloses green environment-friendly light high-strength concrete and a preparation method thereof, wherein the green environment-friendly light high-strength concrete comprises the following dry materials in parts by weight: 700-900 parts of fine aggregate, 300-500 parts of coarse aggregate, 300-500 parts of cement, 100-200 parts of modified fly ash, 20-30 parts of modified fiber and 10-20 parts of water reducing agent. The coarse aggregate is carbonized walnut shells, and the modified fiber is a mixture of modified steel fiber and modified bamboo fiber. The concrete prepared by the invention meets the requirements of light high-strength concrete, simultaneously uses various industrial wastes as raw materials, has the characteristics of environmental protection and resource saving, and simultaneously has good mechanical properties.

Description

Green environment-friendly light high-strength concrete

Technical Field

The invention relates to the technical field of concrete, in particular to green environment-friendly light high-strength concrete.

Background

Along with the improvement of the living standard of people and the progress of the scientific and technological level, the green and environment-friendly building material has been continuously developed from application to the present, and is particularly widely applied to the building industry. Concrete is one of the main materials in the construction industry and is also the main material of buildings. However, the large-scale use of ordinary concrete puts a great strain on the environment when the construction work is carried out. The use of green concrete materials, however, effectively solves this problem. Compared with common concrete materials, the green environment-friendly concrete material has less use of cement, thereby effectively reducing the release of harmful substances in the use process of the cement, realizing the recycling of resources in the use process of the green concrete, and achieving the purposes of low consumption, high quality and environmental protection.

The light high-strength concrete is prepared by adding mineral admixture and additive into cement, light aggregate, light sand and water, and the dry apparent density of the cured concrete is lower than 1950kg/m under the conditions of 20 +/-1 ℃ and 90 percent of relative humidity³Concrete with the compressive strength not lower than 30 MPa. The light high-strength concrete overcomes the defects of the traditional concrete such as self weight and the like, has higher compressive strength compared with the common light concrete, and can meet the requirements of most building structures. Meanwhile, the light high-strength concrete is a porous material, the heat conductivity coefficient and the linear expansion coefficient are greatly lower than those of common concrete, and the heat insulation performance and the fire resistance performance of the light high-strength concrete are more excellent than those of common concrete.

Therefore, the light high-strength concrete prepared by the green and environment-friendly method can protect the environment and save resources, has very important practical significance, and is one of the most important research directions of the concrete at present.

In the present stage, the research idea of green and environment-friendly concrete is mainly to mix industrial waste residues in the concrete in a large amount, namely, on the premise of meeting the performance requirements of constructional engineering, the waste residues generated in the industry are used for replacing the traditional cement clinker in a large amount, and the concrete is prepared by utilizing recyclable aggregate, for example, waste concrete, waste brick mortar and other materials are processed into the aggregate, and then the aggregate and the cement mortar are used for preparing the concrete. Although the methods are environment-friendly, the prepared concrete is difficult to achieve the effects of light weight and high strength, so that the methods and raw materials in the prior art need to be correspondingly modified, and meanwhile, a proper additive is added to achieve the purpose effect.

Patent CN103396064B discloses a green environment-friendly light high-strength powder concrete, and specifically discloses that the main raw materials of the concrete comprise portland cement, silica fume, fly ash, mineral powder, shale ceramic sand, a high-efficiency water reducing agent and water, and the light high-strength powder concrete is obtained by introducing high-strength ceramic sand without using high-cost raw materials such as metal fibers, quartz sand and the like by utilizing the accumulation principle of the powder concrete. The patent does not modify the raw materials, only utilizes the stacking principle of powder concrete to increase the strength of the concrete, and achieves the light effect by using the raw materials with low density, so the obtained concrete has the characteristics of light weight and high strength, but the workability and the stability of the concrete are not good, and the application in practice is influenced.

Patent CN110467394B discloses a lightweight high-strength concrete and a preparation method thereof, and particularly discloses a lightweight high-efficiency concrete which is obtained by mixing sea sand, cement, modified fly ash, modified sepiolite, a silane coupling agent, a polyethyleneimine aqueous solution, a peach gum solution, modified fibers and water. The coal ash and the sepiolite are subjected to lightening treatment mainly by a chemical modification method, and are matched with other additives to enhance the compressive strength, so that the coal ash and the sepiolite have good effects. But most of the raw materials used by the method are not renewable resources, and the environmental protection property of the method is still to be further improved.

Disclosure of Invention

Aiming at the defects in the prior art, the invention aims to provide the concrete which is green and environment-friendly in production raw materials and process, light in weight and high in strength.

In order to solve the technical problems, the invention is realized by the following technical scheme:

a preparation method of green environment-friendly lightweight concrete comprises the following steps: firstly, dry-mixing fine aggregate, coarse aggregate, cement and modified fly ash; then adding water and stirring; then adding modified fiber and stirring; adding water and a water reducing agent, and stirring to obtain concrete mortar; pouring the mortar into a mould, demoulding after forming, and curing to obtain the green environment-friendly lightweight concrete.

Preferably, the green environment-friendly lightweight concrete comprises the following raw materials in parts by weight: 700-900 parts of fine aggregate, 300-500 parts of coarse aggregate, 300-500 parts of cement, 100-200 parts of modified fly ash, 20-30 parts of modified fiber, 10-20 parts of water reducing agent and 150-250 parts of water.

Further preferably, the method comprises the following steps: firstly, adding 700-900 parts of fine aggregate, 300-500 parts of coarse aggregate, 300-500 parts of cement and 100-200 parts of modified fly ash into a stirrer, and stirring at 30-60 rpm for 2-3 min; then adding 90-150 parts of water, and stirring at 30-60 rpm for 2-3 min; then adding 20-30 parts of modified fiber, and stirring at 30-60 rpm for 4-6 min; then adding 60-100 parts of water and 10-20 parts of water reducing agent, stirring at 60-100 rpm for 2-3 min, and finally stirring at 30-60 rpm to obtain concrete mortar; pouring the mortar into a mold, demolding after molding, and curing for 14-28 days under the conditions that the temperature is 20-30 ℃ and the relative humidity is 80-90% to obtain the green environment-friendly lightweight concrete.

Preferably, the fine aggregate is one of river sand, lake sand, mountain sand and desalted sea sand.

Preferably, the coarse aggregate is a carbonized shell.

Further preferably, the coarse aggregate is carbonized walnut shells.

The preparation method of the carbonized walnut shells comprises the following steps:

s1, washing the walnut shells with water, removing residual pulp, and drying to obtain treated walnut shells for later use;

s2, crushing the walnut shells to obtain crushed walnut shells with the particle size of 5-15 mm;

s3, putting the broken walnut shells into a carbonization furnace, heating to 200-250 ℃ at a heating rate of 5-10 ℃/min, preserving heat for 0.5-1 h, heating to 350-550 ℃ at a heating rate of 10-20 ℃/min, preserving heat for 5-8 h, and cooling to 20-30 ℃ to obtain the carbonized walnut shells.

Walnut shells are agricultural solid waste, the main components of which are cellulose, hemicellulose and lignin, and the inventors found that carbonization can cause thermal decomposition and cracking of organic matter (cellulose, hemicellulose and lignin) in the walnut shells. Meanwhile, the swelling and shrinking of the walnut shells can be obviously reduced, and the dimensional stability, the antibiotic property and the surface quality of the walnut shells are improved. The inner surface of the walnut shell is smooth before carbonization, the adhesion between aggregate and mortar is weakened together with the organic matters contained in the walnut shell, so that the strength of concrete is reduced, after carbonization, the inner surface of the walnut shell is also rough, the content of organic matters is reduced, and the strength of concrete is improved; finally, carbonization can fix carbon to the maximum extent, has little pollution to the environment and can further improve the lightweight of concrete.

Preferably, the cement is any one of portland cement, sulfate cement, or aluminate cement.

Preferably, the preparation method of the modified fly ash comprises the following steps: immersing coal ash into 0.5-2 mol/L sulfuric acid water solution, stirring and reacting for 9-12 h at 20-30 ℃, filtering after the reaction is finished, collecting filter residue, washing the filter residue for 2-3 times by using water, and finally drying the washed filter residue for 12-16 h at 100-120 ℃ to obtain the modified coal ash.

The fly ash is the main solid waste discharged by coal-fired power plants and coal gangue and coal slime comprehensive utilization power plants, and the main components of the fly ash are oxides such as silicon dioxide, aluminum oxide, ferric oxide, calcium oxide, magnesium oxide and the like. The main component of the modified fly ash which plays a role in concrete is active silicon dioxide, the modified fly ash is obtained by acidizing the fly ash, metal oxides which are unfavorable for the strength of the concrete can be removed, and meanwhile, the specific surface area of the modified fly ash obtained by treatment is further increased, and micropores are formed. Therefore, the modified fly ash can better play a role in concrete and simultaneously improve the lightweight effect of the concrete.

Preferably, the modified fiber is a modified steel fiber and/or a modified bamboo fiber.

Further preferably, the preparation method of the modified steel fiber comprises the following steps:

m1 completely soaking the steel fiber in 200-500 mL of 0.05-0.1 mol/L calcium chloride aqueous solution containing 1-2 wt% of EDTA, and adjusting the pH value of the aqueous solution to 10-11 by using 0.5-1 mol/L hydrochloric acid or 0.5-1 mol/L sodium hydroxide aqueous solution;

m2 adding 200-500 mL of 0.05-0.1 mol/L sodium carbonate aqueous solution into the solution obtained in the step M1 at a rate of 0.25-0.5 mL/min, and adjusting the pH of the solution to 10-11 by using 0.5-1 mol/L hydrochloric acid or 0.5-1 mol/L sodium hydroxide aqueous solution;

m3, reacting the solution obtained in the step M2 at 20-30 ℃ for 24-72 hours, taking the steel fiber after the reaction is finished, washing the steel fiber with water for 2-3 times, and drying to obtain the calcium carbonate modified steel fiber;

m4 polyethylene glycol and polyphosphoric acid are mixed according to a molar ratio of 1: (1-1.5) mixing, and reacting at 60-90 ℃ for 2-4 h to obtain a mixed solution; and mixing the mixed solution with water according to the mass ratio (90-95): (5-10), and reacting at 60-90 ℃ for 0.5-1 h to obtain polyethylene glycol phosphate;

m5 calcium carbonate modified steel fiber is soaked in polyethylene glycol phosphate ester, and the dosage ratio is 1 g: (10-15) mL, reacting at 130-150 ℃ for 10-20 min, cooling to 20-30 ℃, taking out the steel fiber, washing with water for 2-3 times, and drying to obtain the modified steel fiber.

The preparation method of the modified bamboo fiber comprises the following steps:

n1, soaking the bamboo fibers in 200-500 mL of 2-10 wt% sodium hydroxide aqueous solution, reacting at 20-30 ℃ for 12-24 h, and taking out the bamboo fibers after the reaction is finished and drying to obtain pretreated bamboo fibers for later use;

n2, soaking the pretreated bamboo fiber in 950-1000 mL of 10-20 wt% tetraethyl silicate aqueous solution, adding 20-30 mL of 25-28 wt% ammonia water, reacting at 25-30 ℃ for 4-5 h, taking out the bamboo fiber after the reaction is finished, washing with water for 2-3 times, and drying to obtain the modified bamboo fiber.

Most preferably, the modified fiber is a fiber with a mass ratio of 1: (1-3) mixing the modified steel fiber and the modified bamboo fiber.

The concrete added with the fibers can overcome the defects of low tensile strength, low ultimate elongation and the like of the traditional concrete, and the tensile strength, bending resistance and impact strength of the concrete are improved due to the high tensile strength and high elongation of the fibers, and meanwhile, the concrete can effectively avoid cracking caused by carbonization and shrinkage of the concrete, thereby having very important display significance. The invention selects the common steel fiber and the reproducible bamboo fiber as the raw materials, and improves the performance of the prepared concrete. In order to further improve the reinforcing effect of the fiber, the used steel fiber and bamboo fiber are modified, the surface of the fiber is modified to improve the bonding property of the fiber and concrete or the shape of the fiber is changed to increase the friction and the biting force between the fiber and a matrix.

Compared with common wood, the bamboo fiber has higher strength and toughness, has a reinforcing effect when being added into concrete, is very similar to low-strength steel fiber, is a green and cheap renewable resource, but has obvious defects, such as a large amount of gaps, low wettability, poor moisture resistance, poor bonding property between the fiber and the concrete and the like, and can be degraded under the alkaline condition of the concrete to cause premature failure.

Therefore, the bamboo fiber is soaked in the alkaline solution with a certain concentration for a certain time, the alkaline treatment can promote the removal of partial amorphous components, such as hemicellulose, lignin and cellulose which are soluble in the alkaline solution, the aggregation degree of the fiber is reduced, the surface is rougher, the interface between the matrix and the fiber is increased, and the good adhesive force between the matrix and the bamboo fiber is ensured; and then, silanization modification is carried out on the bamboo fibers after alkali treatment, and the bamboo fibers are more tightly combined with a concrete matrix due to larger specific surface area and rough surface, so that the concrete improvement effect is enhanced.

For the treatment of steel fibers, the inventors propose an effective modification method, namely preparing a layer of calcium carbonate on the surface of the steel fibers, the method has two functions, on one hand, a layer of calcium carbonate is prepared on the surface of the steel fiber, so that the surface of the steel fiber can be rougher, and the calcium carbonate is not directly involved in the hydration process like the active silicon dioxide, but the bonding property of the calcium carbonate and the concrete is obviously higher than that of the steel fiber and the concrete matrix, on the other hand, when the concrete is acted by external force to a certain extent and the steel fiber in the concrete is subjected to sliding displacement, the calcium carbonate coating on the surface thereof is peeled off, the calcium carbonate is broken in the inside thereof, and when the interface region between the steel fiber and the matrix is piled up and rearranged, these calcium carbonate particles fill these gaps and the frictional stress between the interfaces increases again, thereby increasing the pull strength of the steel fibers. The calcium carbonate coating on the surface of the modified steel fiber enhances the improvement effect of the modified steel fiber on concrete from the two aspects.

The inventor selects calcium chloride and sodium carbonate as the treating agents in the preparation process, the calcium carbonate is most easily formed in the solution with the pH value of 10, the concentration, the reaction condition and the time of the treating agents are determined by a large amount of experiments, but the effect is not obvious enough, and the analysis is probably because no matter how to adjust the concentration and the adding sequence, when the reaction time is long, newly-formed calcium carbonate particles with smaller particle diameters on the surface of the steel fiber are gradually dissolved into the surrounding medium due to Oswald ripening, namely, the smaller crystals have higher energy due to larger curvature, and then the surfaces of larger crystal particles are re-precipitated, so when the reaction time is long, the calcium carbonate particles on the surface of the steel fiber are all larger, and when the calcium carbonate particles are larger, the gaps between the steel fiber and the matrix are filled, the gaps can not be completely filled, so that the increase of the frictional stress between the interfaces is insufficient, and the effect is not good; when the treatment time is short, a sufficient amount of calcium carbonate particles cannot be obtained to function.

On the other hand, the inventor adds EDTA with a certain concentration into the reaction system, utilizes the chelation of EDTA on calcium ions, and reduces the effective calcium ion concentration in the solution at the initial stage of the reaction, thereby reducing the actual thermodynamic driving force for nucleation of calcium carbonate and guiding the calcium carbonate to form smaller crystals. Therefore, the calcium carbonate particles with smaller particle size can be well filled in the gap between the steel fiber and the concrete matrix, thereby remarkably increasing the frictional stress between the interfaces.

The inventor thinks that since the lightweight concrete is required to be prepared by the present invention, most of the raw materials are processed to be lightweight, and although the density of the concrete can be reduced while maintaining the strength, the concrete has more pores, which leads to a significant reduction in the ion permeation resistance of the concrete, and particularly, steel fibers incorporated in the concrete are affected by ion permeation, which leads to a reduction in the strength of the concrete, among which chloride ions are most influential on the steel fibers. In this kind of strong alkaline environment of concrete, steel fibre is comparatively stable, is difficult for taking place the corrosion, but when a large amount of chloride ions permeate, can corrode the passive film on steel fibre surface, forms the corruption battery on steel fibre surface, and in addition the depolarization effect and the effect of arriving of chloride ions have accelerated steel fibre's corruption, not only lead to its intensity to descend, still can lead to the cohesion reduction with the concrete.

In order to solve the problem, the inventor carries out further improvement on the basis of calcium carbonate modified steel fibers, calcium carbonate on the surface of the steel fibers is subjected to phosphorylation modification by using polyethylene glycol phosphate, so that the compactness of a coating is further improved, and the steric hindrance effect of polyethylene glycol on the surface can slow down the penetration effect of chloride ions, so that the concentration of the chloride ions on the surface of the steel fibers is reduced, and the risk of corrosion of the steel fibers is reduced; meanwhile, even if the steel fiber coating is damaged under the action of strong external force, the polyethylene glycol can release phosphate ions according to phosphate ester in the concrete, so that the phosphate and iron can generate complex phosphorylation reaction to generate an insoluble phosphoric acid film to be deposited on the surface of the steel fiber, the corrosion of the steel fiber is prevented, the corrosion of chloride ions to the steel bar when the concrete is mixed with the steel bar can be reduced, and a good technical effect is achieved.

Preferably, the water reducing agent is a polycarboxylic acid water reducing agent.

The invention has the beneficial effects that:

1. compared with the prior art, the invention greatly uses environment-friendly materials such as walnut shells, fly ash, bamboo fibers and other raw materials in the selection of the raw materials, effectively utilizes the raw materials through modification, and has the characteristic of environmental protection.

2. Compared with the prior art, in the aspect of modification of raw materials, on one hand, the performance of the concrete is improved, on the other hand, the raw materials are subjected to light treatment, and the prepared concrete reaches the standard of light weight and high strength.

3. Compared with the prior art, the invention provides the method for preparing the layer of calcium carbonate with smaller particle size on the surface of the steel fiber, and the modified steel fiber is applied to the concrete, so that the bonding property of the steel fiber and the matrix interface of the concrete can be improved, and the gaps can be filled when the interface area between the steel fiber and the matrix is stacked and rearranged, thereby enhancing the improvement effect of the steel fiber on the concrete performance from the two aspects.

Detailed Description

The experimental procedures used in the following examples are all conventional procedures unless otherwise specified.

Materials, reagents and the like used in the following examples are commercially available unless otherwise specified.

The specific parameters of some substances and instruments in the embodiment of the invention are as follows:

portland cement, P.O 42.5.5R, loss on ignition of less than 4.24%, was purchased from England Cement, Inc., Anhui.

River sand, the mud content is less than or equal to 0.1 percent, and is purchased from Guizhou Baoli co-construction materials, Inc.

Fly ash, first grade ash, was purchased from kning Hengzhi New building materials, Inc.

The steel fiber is of a shear type, has the length of 35mm, the width of 1.5mm, the thickness of 0.7mm and the tensile strength of 400MPa, and is purchased from Hebei Hezhou shui Fengyuan geotechnical materials Co.

The bamboo fiber has the average length of 75mm, the average fineness of 0.1mm and the moisture regain of 10 percent and is purchased from bamboo science and technology development ltd of Fujian Jianzhou.

Polyphosphoric acid, CAS No. 8017-16-1, with a content of 85% or more, was purchased from Shanghai Michelin Biotechnology Ltd.

Polyethylene glycol, average molecular weight 2000, available from Shanghai Michelin Biochemical technology, Inc.

The polycarboxylic acid water reducing agent is an industrial grade water reducing agent, has the chloride ion content of less than 0.03 percent and is purchased from Shandong New geodetic industry group company Limited.

Example 1

The preparation method of the green environment-friendly light high-strength concrete comprises the following steps: firstly, adding 800 parts of river sand, 400 parts of carbonized walnut shells, 450 parts of Portland cement and 100 parts of modified fly ash into a stirrer, and stirring for 2min at 60 rpm; then 108 parts of water are added, and the mixture is stirred for 2min at 60 rpm; then adding 20 parts of modified fiber, and stirring at 60rpm for 4 min; then adding 72 parts of water and 10 parts of polycarboxylic acid water reducing agent, stirring at 100rpm for 2min, and finally stirring at 60rpm to obtain concrete mortar; pouring the mortar into an oil-coated 150mm multiplied by 150mm plastic mould, compacting by vibration, covering an upper opening of the mould with a plastic film to prevent evaporation loss of water, taking out the concrete module from the mould after 24h at the temperature of 20 ℃ and the relative humidity of 90%, and curing for 28d under the same temperature and humidity to obtain the green environment-friendly light high-strength concrete.

s2 crushing the walnut shells to obtain crushed walnut shells with the particle size of 10 +/-3 mm;

s3, putting the crushed walnut shells into a carbonization furnace, heating to 200 ℃ at a heating rate of 10 ℃/min, keeping the temperature for 1h, heating to 550 ℃ at a heating rate of 20 ℃/min, keeping the temperature for 5h, and cooling to 25 ℃ to obtain carbonized walnut shells;

the preparation method of the modified fly ash comprises the following steps: immersing coal ash in 1.5mol/L sulfuric acid aqueous solution, stirring and reacting for 12h at 25 ℃, filtering after the reaction is finished, collecting filter residue, washing the filter residue for 3 times by using water, and finally drying the washed filter residue for 12h at 120 ℃ to obtain modified coal ash;

the modified fiber is prepared from the following components in percentage by mass: 3, mixing the modified steel fiber and the modified bamboo fiber;

the preparation method of the modified steel fiber comprises the following steps:

m1 steel fiber was completely immersed in 200mL of 0.05mol/L calcium chloride aqueous solution containing 1 wt% EDTA, and the pH of the solution was adjusted to 10 with 0.5mol/L aqueous sodium hydroxide solution;

m2, adding 200mL of 0.05mol/L sodium carbonate aqueous solution into the solution obtained in the step M1 at a rate of 0.25mL/min, and adjusting the pH of the solution to 10 by using 0.5mol/L sodium hydroxide aqueous solution;

m3, placing the solution obtained in the step M2 at 25 ℃ for reaction for 72 hours, taking the steel fiber after the reaction is finished, washing the steel fiber for 3 times by using water, and drying the steel fiber to obtain calcium carbonate modified steel fiber;

m4 polyethylene glycol and polyphosphoric acid are mixed according to a molar ratio of 1: 1.3, and reacting for 3 hours at 80 ℃ to obtain a mixed solution; and mixing the mixed solution with water according to a mass ratio of 95: 5, mixing, and reacting at 80 ℃ for 1h to obtain polyethylene glycol phosphate;

m5 calcium carbonate modified steel fiber is soaked in polyethylene glycol phosphate ester, and the dosage ratio is 1 g: 15mL, reacting at 140 ℃ for 20min, cooling to 25 ℃, taking out the steel fiber, washing with water for 3 times, and drying to obtain the modified steel fiber;

n1, soaking the bamboo fiber in 200mL of 6 wt% sodium hydroxide aqueous solution, reacting for 12h at 25 ℃, taking out the bamboo fiber after the reaction is finished, and drying to obtain pretreated bamboo fiber for later use;

n2 soaking the pretreated bamboo fiber in 1000mL of 15 wt% tetraethyl silicate aqueous solution, then adding 20mL of 28 wt% ammonia water, reacting at 25 ℃ for 4h, taking out the bamboo fiber after the reaction is finished, washing with water for 3 times, and drying to obtain the modified bamboo fiber.

Example 2

The preparation method of the green environment-friendly light high-strength concrete comprises the following steps: firstly, adding 800 parts of river sand, 400 parts of carbonized walnut shells, 450 parts of Portland cement and 100 parts of modified fly ash into a stirrer, and stirring for 2min at 60 rpm; then 108 parts of water are added, and the mixture is stirred for 2min at 60 rpm; then adding 20 parts of modified steel fiber, and stirring at 60rpm for 4 min; then adding 72 parts of water and 10 parts of polycarboxylic acid water reducing agent, stirring at 100rpm for 2min, and finally stirring at 60rpm to obtain concrete mortar; pouring the mortar into an oil-coated 150mm multiplied by 150mm plastic mould, compacting by vibration, covering an upper opening of the mould with a plastic film to prevent evaporation loss of water, taking out the concrete module from the mould after 24h at the temperature of 20 ℃ and the relative humidity of 90%, and curing for 28d under the same temperature and humidity to obtain the green environment-friendly light high-strength concrete.

s2 crushing the walnut shells into walnut shells with the particle size of 10 +/-3 mm;

m2 adding 200mL of 0.05mol/L sodium carbonate aqueous solution into the solution obtained in the step M1 at a rate of 0.25mL/min, and adjusting the pH of the solution to 10 by using 0.5mol/L sodium hydroxide aqueous solution;

m4 polyethylene glycol and polyphosphoric acid are mixed according to a molar ratio of 1: 1.3, mixing, and reacting for 3 hours at 80 ℃ to obtain a mixed solution; and mixing the mixed solution with water according to a mass ratio of 95: 5, mixing, and reacting at 80 ℃ for 1h to obtain polyethylene glycol phosphate;

m5 calcium carbonate modified steel fiber is soaked in polyethylene glycol phosphate ester, and the dosage ratio is 1 g: 15mL, reacting at 140 ℃ for 20min, cooling to 25 ℃, taking out the steel fiber, washing with water for 3 times, and drying to obtain the modified steel fiber.

Example 3

The preparation method of the green environment-friendly light high-strength concrete comprises the following steps: firstly, adding 800 parts of river sand, 400 parts of carbonized walnut shells, 450 parts of Portland cement and 100 parts of modified fly ash into a stirrer, and stirring for 2min at 60 rpm; then 108 parts of water are added, and the mixture is stirred for 2min at 60 rpm; then adding 20 parts of modified bamboo fiber, and stirring at 60rpm for 4 min; then adding 72 parts of water and 10 parts of polycarboxylic acid water reducing agent, stirring at 100rpm for 2min, and finally stirring at 60rpm to obtain concrete mortar; pouring the mortar into an oil-coated 150mm multiplied by 150mm plastic mould, compacting by vibration, covering an opening on the mould with a plastic film to prevent evaporation loss of water, taking out the concrete module from the mould after 24h at the temperature of 20 ℃ and the relative humidity of 90%, and curing for 28d under the same temperature and humidity to obtain green environment-friendly light high-strength concrete;

Example 4

The preparation method of the green environment-friendly light high-strength concrete comprises the following steps: firstly, adding 800 parts of river sand, 400 parts of carbonized walnut shells, 450 parts of Portland cement and 100 parts of modified fly ash into a stirrer, and stirring for 2min at 60 rpm; then 108 parts of water are added, and the mixture is stirred for 2min at 60 rpm; then adding 20 parts of calcium carbonate modified steel fiber, and stirring at 60rpm for 4 min; then adding 72 parts of water and 10 parts of polycarboxylic acid water reducing agent, stirring at 100rpm for 2min, and finally stirring at 60rpm to obtain concrete mortar; pouring the mortar into an oil-coated 150mm multiplied by 150mm plastic mould, compacting by vibration, covering an opening on the mould with a plastic film to prevent evaporation loss of water, taking out the concrete module from the mould after 24h at the temperature of 20 ℃ and the relative humidity of 90%, and curing for 28d under the same temperature and humidity to obtain green environment-friendly light high-strength concrete;

the preparation method of the calcium carbonate modified steel fiber comprises the following steps:

m3, placing the solution obtained in the step M2 at 25 ℃ for reaction for 72 hours, taking the steel fiber after the reaction is finished, washing the steel fiber with water for 3 times, and drying to obtain the calcium carbonate modified steel fiber.

Example 5

The preparation method of the green environment-friendly light high-strength concrete comprises the following steps: firstly, adding 800 parts of river sand, 400 parts of carbonized walnut shells, 450 parts of Portland cement and 100 parts of fly ash into a stirrer, and stirring for 2min at 60 rpm; then 108 parts of water are added, and the mixture is stirred for 2min at 60 rpm; then adding 20 parts of modified fiber, and stirring at 60rpm for 4 min; then adding 72 parts of water and 10 parts of polycarboxylic acid water reducing agent, stirring at 100rpm for 2min, and finally stirring at 60rpm to obtain concrete mortar; pouring the mortar into an oil-coated 150mm multiplied by 150mm plastic mould, compacting by vibration, covering an opening on the mould with a plastic film to prevent evaporation loss of water, taking out the concrete module from the mould after 24h at the temperature of 20 ℃ and the relative humidity of 90%, and curing for 28d under the same temperature and humidity to obtain green environment-friendly light high-strength concrete;

m4 polyethylene glycol and polyphosphoric acid are mixed according to the mol ratio of 1: 1.3, mixing, and reacting for 3 hours at 80 ℃ to obtain a mixed solution; and mixing the mixed solution with water according to a mass ratio of 95: 5, mixing, and reacting at 80 ℃ for 1h to obtain polyethylene glycol phosphate;

Example 6

The preparation method of the green environment-friendly light high-strength concrete comprises the following steps: firstly, adding 800 parts of river sand, 400 parts of walnut shells, 450 parts of portland cement and 100 parts of modified fly ash into a stirrer, and stirring for 2min at 60 rpm; then 108 parts of water are added, and the mixture is stirred for 2min at 60 rpm; then adding 20 parts of modified fiber, and stirring at 60rpm for 4 min; then adding 72 parts of water and 10 parts of polycarboxylic acid water reducing agent, stirring at 100rpm for 2min, and finally stirring at 60rpm to obtain concrete mortar; pouring the mortar into an oil-coated 150mm multiplied by 150mm plastic mould, compacting by vibration, covering an opening on the mould with a plastic film to prevent evaporation loss of water, taking out the concrete module from the mould after 24h at the temperature of 20 ℃ and the relative humidity of 90%, and curing for 28d under the same temperature and humidity to obtain green environment-friendly light high-strength concrete;

the preparation method of the modified fly ash comprises the following steps: immersing coal ash in 1.5mol/L sulfuric acid aqueous solution, stirring and reacting for 12 hours at 25 ℃, filtering after the reaction is finished, collecting filter residue, washing the filter residue with water for 3 times, and finally drying the washed filter residue for 12 hours at 120 ℃ to obtain modified coal ash;

Test example 1

Testing concrete density: the mass of the concrete modules of the above examples was weighed and the density calculated, 3 replicates of each example sample were taken and the results averaged. The test results are shown in table 1.

TABLE 1 concrete density

	Density (kg/m)³)
		Example 1	1727
Example 2	1743
		Example 3	1701
Example 4	1747
		Example 5	1821
Example 6	1735

From the results, it is understood that the density of all the above examples is less than 1950kg/m³And meets the condition of light concrete. In the modification of the raw materials, except that the walnut shells serving as the coarse aggregates are carbonized to obviously reduce the density of the concrete, the modification of the fly ash and the modification of the fibers have little influence on the density of the concrete, but the reduction is small. The steel fiber can obviously improve the density of concrete compared with the bamboo fiber, but the actual influence is not great because the mixing amount is not large. In summary, the raw materials selected by the invention and the concrete prepared by the preparation method can reach the requirement of lightweight concreteAnd (5) obtaining.

Test example 2

Testing the mechanical property of the concrete: the concrete modules prepared in the embodiments are tested for mechanical property according to GB/T50081-2002 Standard of test methods for mechanical property of common concrete:

testing and calculating the compressive strength of the concrete according to the standard section 6;

testing and calculating the splitting tensile strength of the concrete according to the standard section 9;

the results obtained are shown in table 2.

TABLE 2 mechanical Properties of the concretes

As is clear from the analysis of the results shown in Table 2, the mechanical properties of the examples were all the best, and the compressive strength and the tensile strength at split were 56.4MPa and 5.45MPa, respectively.

Compared with the concrete with only one kind of modified fiber, the concrete with the added modified steel fiber and the modified bamboo fiber in a certain proportion has improved compressive strength and splitting tensile strength, especially splitting tensile strength, which is probably caused by the synergistic effect generated by the simultaneous addition of the two kinds of fiber, because the modification modes of the two kinds of fiber are different, the mechanism for improving the tensile performance of the concrete is also different, when the two kinds of fiber are added simultaneously, the active silica coating on the surface of the modified bamboo fiber can directly react with calcium hydroxide generated in the hydration process of cement, so that the bamboo fiber and the concrete matrix have good adhesive property, therefore, in the preparation process of concrete stirring, the modified bamboo fiber and the modified steel fiber possibly have certain hydrophobicity on the surface, thereby generating the winding and crosslinking effects, therefore, the modified steel fiber and the bamboo fiber are in a cross-linked state in the concrete matrix, the bamboo fiber is wound on the surface of the steel fiber, so that the bonding force between the steel fiber and the concrete interface can be improved, and the bamboo fiber is also subjected to the physical winding effect of the bamboo fiber, so that the modified steel fiber inside the concrete is less prone to sliding under the action of external force, and the tensile property better than that of singly added modified steel fiber or modified bamboo fiber is achieved. Therefore, the modified bamboo fiber and the modified steel fiber which are added in a certain proportion have obvious synergistic effect on improving the strength of concrete.

It is worth noting that the difference between example 2 and example 4, the modified steel fiber used in example 2, and the calcium carbonate modified steel fiber used in example 4, is that the compressive strength and the tensile strength at split are significantly higher than those of example 2, which is probably because the adhesion between the calcium carbonate modified steel fiber and the concrete interface is better than that of the modified steel fiber, because the polyethylene glycol on the surface of the modified steel fiber increases the hydrophobicity of the steel fiber, and the adhesion between the modified steel fiber and the concrete interface is reduced due to the steric hindrance, thereby reducing the strength of the concrete. In example 1, the modified steel fiber and the modified bamboo fiber are mixed according to a certain ratio and added, so that the defect is improved through a synergistic effect.

The only difference between example 5 and example 1 is that the walnut shells are not carbonized, and it can be seen that the compressive strength and the cleavage tensile strength are both significantly reduced, and the cause of this is probably that the walnut shells act as the aggregate of the concrete and play a role in supporting and stabilizing the concrete, but if the walnut shells are not directly added without treatment, because the walnut shells contain a large amount of hydrophilic groups and biomass, the compatibility with the cement is poor, and the inner surfaces of the walnut shells are too smooth, gaps exist between the walnut shells and the interface, the interface binding force is not strong, sliding and cracking easily occur under the action of external force, and the biomass contained in the walnut shells is degraded by the alkaline condition or microorganism of the concrete, so that the support performance is significantly reduced, therefore, the walnut shells are carbonized, not only can solve the above problems, but also remove the components affecting the concrete performance, and further lightweight concrete.

Example 6 differs from example 1 in that the compression resistance and the tensile strength of the unmodified fly ash used are reduced to some extent compared with the example, and the reduction degree is not large, which may be because the modified fly ash mainly removes some impurities which do not participate in the hydration process and are harmful to the concrete, and at the same time, the fly ash has a larger specific surface area, and the reaction is more complete in the preparation of the concrete, so as to achieve the purpose of cement lightening and resource saving.

Test example 3

And (3) testing the chloride ion corrosion resistance: after 30 corrosion cycles are respectively carried out on the concrete modules in the embodiments 1-4, the concrete is soaked in 6% sodium chloride water solution for 12 hours at the temperature of 20 ℃, the concrete is dried for 12 hours, the one-time corrosion cycle is adopted, the splitting tensile strength of the concrete is tested according to the method for testing the splitting tensile strength in the test example 2, and the change difference between the concrete before corrosion and the concrete after corrosion is compared;

the results obtained are shown in Table 3.

TABLE 3 chloride ion Corrosion resistance test

The results in Table 3 are analyzed to show that the influence of chloride ions on the splitting tensile strength of concrete mainly acts on steel fibers, the influence on the concrete only using the modified bamboo fibers in example 3 is not great, the influence on the concrete only using the calcium carbonate modified steel fibers in example 4 is the greatest, and the splitting tensile strength after corrosion is reduced by 0.31 MPa; the steel fibers used in the examples 1 and 2 are both modified steel fibers, the reduction of the tensile strength of the split is low after corrosion, which shows that the chlorine ion corrosion resistance of concrete is remarkably improved by modifying the steel fibers, and the reduction degree of the example 1 is smaller than that of the example 2, which shows that the crosslinking between the modified bamboo fibers and the modified steel fibers can also prevent the corrosion effect of chlorine ions on the steel fibers through the steric hindrance effect. Therefore, the chlorine ion corrosion resistance of the concrete can be obviously improved by modifying the steel fibers and adding the modified bamboo fibers in a compounding way, so that the application range of the invention is expanded.

In conclusion, the invention provides the green environment-friendly light-weight high-strength concrete and the preparation method thereof, a large amount of waste materials of other industries are selected, resources are saved, the environment is protected, meanwhile, in the process of the invention, a plurality of modification methods for raw materials are provided, and certain inspiration can be provided for the preparation of other types of concrete.

Claims

1. A preparation method of green environment-friendly lightweight concrete is characterized by comprising the following steps: the method comprises the following steps: firstly, dry-mixing fine aggregate, coarse aggregate, cement and modified fly ash; then adding water and stirring; then adding modified fiber and stirring; adding water and a water reducing agent, and stirring to obtain concrete mortar; pouring the mortar into a mould, demoulding after forming, and curing to obtain the green environment-friendly lightweight concrete.

2. The method of claim 1, wherein: the method comprises the following steps: firstly, adding 700-900 parts of fine aggregate, 300-500 parts of coarse aggregate, 300-500 parts of cement and 100-200 parts of modified fly ash into a stirrer, and stirring at 30-60 rpm for 2-3 min; then adding 90-150 parts of water, and stirring at 30-60 rpm for 2-3 min; then adding 20-30 parts of modified fiber, and stirring at 30-60 rpm for 4-6 min; then adding 60-100 parts of water and 10-20 parts of water reducing agent, stirring at 60-100 rpm for 2-3 min, and finally stirring at 30-60 rpm to obtain concrete mortar; pouring the mortar into a mold, demolding after molding, and curing for 14-28 days under the conditions that the temperature is 20-30 ℃ and the relative humidity is 80-90% to obtain the green environment-friendly lightweight concrete.

3. The method of claim 1, wherein: the coarse aggregate is carbonized walnut shells.

4. The method of claim 3, wherein: the preparation method of the carbonized walnut shells comprises the following steps:

s3, putting the crushed walnut shells into a carbonization furnace, heating to 200-250 ℃ at a heating rate of 5-10 ℃/min, preserving heat for 0.5-1 h, heating to 350-550 ℃ at a heating rate of 10-20 ℃/min, preserving heat for 5-8 h, and cooling to 20-30 ℃ to obtain the carbonized walnut shells.

5. The method of claim 1, wherein: the cement is any one of portland cement, sulfate cement or aluminate cement.

6. The method of claim 1, wherein: the modified fiber is modified steel fiber and/or modified bamboo fiber.

7. The method of claim 6, wherein: the preparation method of the modified steel fiber comprises the following steps:

m1 completely soaking the steel fiber in 200-500 mL of 0.05-0.1 mol/L calcium chloride aqueous solution containing 1-2 wt% of EDTA, and adjusting the pH value of the solution to 10-11 by using 0.5-1 mol/L sodium hydroxide aqueous solution;

m2, adding 200-500 mL of 0.05-0.1 mol/L sodium carbonate aqueous solution into the solution obtained in the step M1 at the rate of 0.25-0.5 mL/min, and adjusting the pH value of the solution to 10-11 by using 0.5-1 mol/L sodium hydroxide aqueous solution;

m3, placing the solution obtained in the step M2 at 20-30 ℃ for reaction for 24-72 hours, taking steel fibers after the reaction is finished, washing the steel fibers for 2-3 times with water, and drying to obtain calcium carbonate modified steel fibers;

m5 calcium carbonate modified steel fiber is soaked in polyethylene glycol phosphate ester, and the dosage ratio is 1 g: (10-15) mL, reacting at 130-150 ℃ for 10-20 min, cooling to 20-30 ℃, taking out the calcium carbonate modified steel fiber, washing with water for 2-3 times, and drying to obtain the modified steel fiber.

8. The method of claim 6, wherein: the preparation method of the modified bamboo fiber comprises the following steps:

n2, soaking the pretreated bamboo fiber in 950-1000 mL of 10-20 wt% tetraethyl silicate aqueous solution, adding 20-30 mL of 25-28 wt% ammonia water, reacting at 25-30 ℃ for 4-5 h, taking out the pretreated bamboo fiber after the reaction is finished, washing with water for 2-3 times, and drying to obtain the modified bamboo fiber.

9. The method of claim 1 or 6, wherein: the modified fiber is prepared from the following components in percentage by mass: (1-3) mixing the modified steel fiber and the modified bamboo fiber.

10. A green environmental-friendly lightweight concrete prepared by the preparation method of any one of claims 1 to 9.